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# 1  
Old 12-11-2009
Help with sed substitution

I'm a noob to unix, and I have a line of data like the following:
title=Boston|tcolor=green|desc=Large city in New England|url=www.boston.com

Is there a way to change a field value with sed substitution?
(i.e. change tcolor=green to tcolor=blue)

I figured out: sed 's/tcolor=.*|/tcolor=blue|/'

...but because of the whole greedy thing, it replaces everything from tcolor= up until the last "|"


For a bit of context, the entire script gets passed values for $title, $tcolor, $desc, and $url... if $title matches a data item that already has that title, than I have to update its other fields to the new values.

I hope that all makes sense.... i appreciate any hints you can give me! :-)
# 2  
Old 12-11-2009
For starters you could use this:
Code:
sed 's/tcolor=[^|]*/tcolor=blue/'

-or-
Code:
sed 's/\(tcolor=\)[^|]*/\1blue/'

# 3  
Old 12-11-2009
don't use sed to parse structured data. you have "|" delimiting your data, therefore, you can split on "|" to get each field. Tools like awk does this job well
Code:
echo $title|awk -F"|" '{for(i=1;i<=NF;i++){if($i~/^tcolor/){$i="tocolor=blue"}};print  }' OFS="|"
Boston|tocolor=blue|desc=Large city in New England|url=www.boston.com



---------- Post updated at 09:31 PM ---------- Previous update was at 09:28 PM ----------

Quote:
Originally Posted by Scrutinizer
For starters you could use this:
Code:
sed 's/tcolor=[^|]*/tcolor=blue/'

-or-
Code:
sed 's/\(tcolor=\)[^|]*/\1blue/'

sed regex is greedy. anyway to make it non greedy and it would be a perfect sed answer Smilie
# 4  
Old 12-12-2009
Hi ghostdog. Not sure what you mean. I made it non-greedy by using [^|]* , no?
Quote:
don't use sed to parse structured data.
I disagree with such a black and white rule. It depends.

Last edited by Scrutinizer; 12-12-2009 at 03:25 AM..
# 5  
Old 12-12-2009
hi
what i meant is, say if the data look like this, 2 "tocolor=green"
Code:
title="Boston|tcolor=green|desc=Large city in New England|url=www.boston.com|tcolor=green"

then the sed command will only change it to blue once. It should be twice.
Code:
# echo $title|sed 's/\(tcolor=\)[^|]*/\1blue/'
Boston|tcolor=blue|desc=Large city in New England|url=www.boston.com|tcolor=green

# 6  
Old 12-12-2009
OK, but that is both hypothetical since the OP did not specify this, and not very typical anyway to have two fields with the same description.

And even if it were the case the sed solution would make this quite controllable.
Code:
$ line='Boston|tcolor=green|desc=Large city in New England|url=www.boston.com|tcolor=green'

$ echo "$line"| sed 's/\(tcolor=\)[^|]*/\1blue/'
Boston|tcolor=blue|desc=Large city in New England|url=www.boston.com|tcolor=green

$ echo "$line"| sed 's/\(tcolor=\)[^|]*/\1blue/2'
Boston|tcolor=green|desc=Large city in New England|url=www.boston.com|tcolor=blue

$ echo "$line"| sed 's/\(tcolor=\)[^|]*/\1blue/g'
Boston|tcolor=blue|desc=Large city in New England|url=www.boston.com|tcolor=blue


Last edited by Scrutinizer; 12-12-2009 at 03:54 AM..
# 7  
Old 12-12-2009
Quote:
Originally Posted by Scrutinizer
OK, but that is both hypothetical since the OP did not specify this, and not very typical anyway to have two fields with the same description.

And even if it were the case the sed solution would make this quite controllable.
Code:
$ line='Boston|tcolor=green|desc=Large city in New England|url=www.boston.com|tcolor=green'

$ echo "$line"| sed 's/\(tcolor=\)[^|]*/\1blue/'
Boston|tcolor=blue|desc=Large city in New England|url=www.boston.com|tcolor=green

$ echo "$line"| sed 's/\(tcolor=\)[^|]*/\1blue/2'
Boston|tcolor=green|desc=Large city in New England|url=www.boston.com|tcolor=blue

$ echo "$line"| sed 's/\(tcolor=\)[^|]*/\1blue/g'
Boston|tcolor=blue|desc=Large city in New England|url=www.boston.com|tcolor=blue

yes, its hypothetical, but anything is possible. And then comes the part i am asking: non greediness
Code:
$ title="Boston|tcolor=green|desc=Large city in New England|url=www.boston.com|tcolor=green|setcolor=green"
$ echo $title|sed 's/\(tcolor=\)[^|]*/\1blue/g'
Boston|tcolor=blue|desc=Large city in New England|url=www.boston.com|tcolor=blue|setcolor=blue

take care of that, and it should be perfect sed solution

---------- Post updated at 03:25 AM ---------- Previous update was at 03:16 AM ----------

Quote:
Originally Posted by Scrutinizer
I disagree with such a black and white rule. It depends.
you don't have to agree with me. I just don't waste my time crafting complex regex that is hard to read and debug when I can do things more easily.
 

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